Abstract

Common envelope is the most important evolutionary process in the formation of all close compact binaries. It is well known that during the common envelope phase a fraction of the orbital energy is used to expel the envelope. However, it is not clear yet whether or not additional energy sources, such as the recombination energy of the envelope, play a decisive role. Here we demonstrate that recombination energy can only be considered as important if close binaries containing high-mass white dwarfs (M-wd greater than or similar to 0.8M(circle dot)) at relatively long orbital periods (P-orb greater than or similar to 1-3 days) exist.